Field of the Invention
The present invention relates to a driving apparatus, and more particularly, to a driving apparatus configured to drive a lens, and a lens apparatus and an image pickup apparatus including the lens driving apparatus.
Description of the Related Art
When a lens is to be driven by a drive apparatus, a lens position is detected by a position detector, and a control signal for eliminating a difference between the detected position and a target position determined based on a position command value is transmitted to a motor, to thereby drive the lens toward the target position (position feedback control). Further, a lens speed determined based on the position detected by the position detector is reflected on a value to be output to the motor, to thereby drive the lens at a constant speed (speed feedback control).
However, the position detector configured to detect the lens position is influenced by a backlash of a gear train of a lens driving mechanism, and hence the rotational position and rotational speed of a motor derived based on detection results of the position detector are inaccurate. Thus, when the rotational speed of motor is to be controlled based on the detection signal, an unintended control signal is transmitted to the motor.
In particular, when the lens is to be operated in a reverse direction, the position detector does not generate any signal immediately due to the backlash. A drive signal is continuously transmitted to the motor until the backlash is eliminated and then a signal is generated by the position detector. As a result, the rotational speed of motor is increased excessively, which may cause an operator to feel uncomfortable with an image at the start of lens movement.
In Japanese Patent Application Laid-Open No. H04-060508, the following system is disclosed. This system includes a first pulse generator configured to generate a pulse in response to lens movement, and a second pulse generator configured to generate a pulse in response to motor drive. The system is configured to control the drive amount of the lens based on an output from the first pulse generator, and to control the rotational speed of motor based on an output from the second pulse generator. Thus, accurate lens drive control is performed without the influence of the backlash of the gear train of the lens driving mechanism.
According to the related art disclosed in Japanese Patent Application Laid-Open No. H04-060508, however, the lens position and the rotational position of motor are detected by separate position detectors. Therefore, at least two position detectors are necessary to control a single movable optical member, thereby raising such problems that the apparatus is upsized and the manufacturing cost is increased.